Your car gets 24 miles per gallon (mpg) at 60 miles per hour (mph) and 20 mpg at 70 mph. At what speed should you make a 500-mile trip: (a) If gas costs $3 per gallon and your time is worth $18/hr? (b) If gas costs $4 per gallon and your time is worth $12/hr? (c) If gas costs $5 per gallon and your time is worth $9/hr? (d) Build a spreadsheet (sec Appendix A) to calculate the total trip cost for gas costs of $2, $3, $4, and $5 and values of time of $6, $9, $12, $15, and $ 18 per hour. Do two tables: one at 60 mph and one at 70 mph.